Thévenin equivalent based static contingency assessment

Abstract

The present invention relates to a method for static security assessment of a power system and a real time static security assessment system for assessing a power system, the power system having a plurality of generators, the plurality of generators being represented in the network by a plurality of voltage controlled nodes, wherein the method for static security assessment of the power system comprises receiving information of a present state of the power system, determining a Thevenin equivalent for each voltage controlled node, determining for each voltage controlled node on basis of the determined present state of the power system and determining a first representation of the network based on the determined Thevenin equivalents, determining a modified representation of the network, wherein the modified representation is a representation of the network having at least one contingency, wherein at least one Thevenin equivalent of at least one voltage controlled node is modified due to the at least one contingency, the modified network representation being determined on the basis of the modified Thevenin equivalents, calculating voltage angles of the modified Thevenin equivalents, and evaluating the voltage angles to determine whether the network having at least one contingency admit a steady state. Also a method of providing information on a real time static security assessment of a power system is disclosed.

1 . A method for conducting contingency analyses in static security assessment of a power system, the power system having a plurality of generators injecting power into a network having a plurality of nodes and a plurality of branches, the plurality of generators being represented in the network by a plurality of voltage controlled nodes, the method comprising:
 receiving information of a present state of the power system,   determining a Thévenin equivalent for each voltage controlled node, wherein a Thévenin equivalent is determined for each voltage controlled node on the basis of the determined present state of the power system,   determining a representation of the network based on the determined Thévenin equivalents,   applying at least one contingency to the network,   determining a modified representation of the network, wherein the modified network representation is a representation of the network having at least one applied contingency, wherein at least one Thévenin equivalent of at least one voltage controlled node is modified due to the at least one applied contingency, the modified network representation being determined on the basis of the modified Thévenin equivalents,   calculating voltage angles of the modified Thévenin equivalents, and   evaluating the voltage angles to determine whether the network having at least one applied contingency admits a steady state.   
     
     
         2 - 17 . (canceled) 
     
     
         18 . The method according to  claim 1 , wherein the representation of the network is based on a two-source equivalent, wherein the two-source equivalent comprises the determined Thévenin equivalent and a voltage phasor of the voltage controlled node. 
     
     
         19 . The method according to  claim 1 , wherein the method comprises evaluating whether the application of the contingency results in a stable network condition. 
     
     
         20 . The method according to  claim 1 , wherein the at least one contingency is a topological change to the network. 
     
     
         21 . The method according to  claim 1 , wherein the at least one contingency is a broken transmission line grid, a loss of a single transmission line, a loss of a generator, a damaged generator and/or any fault that provide a fault to the power system that may result in an unstable power system. 
     
     
         22 . The method according to  claim 1 , wherein voltages at voltage controlled nodes and/or at non-controlled voltage nodes are compared against operational limits. 
     
     
         23 . The method according to  claim 1 , wherein the calculation of the Thévenin equivalent for each voltage controlled node is performed assuming a constant active power injection and constant voltage magnitudes for each voltage controlled node. 
     
     
         24 . The method according to  claim 1 , wherein a grid transformation matrix comprises calculated Thévenin voltages for each voltage controlled node, one or more corresponding grid transformation coefficients and one or more corresponding voltages of voltage controlled nodes and/or wherein a grid transformation coefficient is a relation between the Thévenin equivalent voltage at a voltage controlled node and voltage phasors at neighbouring voltage controlled nodes. 
     
     
         25 . The method according to  claim 22 , wherein the determined Thévenin equivalents on which the first network representation is based corresponds to Thévenin equivalents on which the modified network representation is based in at least the part of the modified network representation corresponding to a part of the first network representation. 
     
     
         26 . The method according to  claim 1 , wherein the step of determining a present state of the power system comprises obtaining synchronized Phasor Measurement Unit measurements from a plurality of nodes of the power system. 
     
     
         27 . The method according to  claim 1 , wherein the Thévenin equivalents, the modified Thévenin equivalents and/or the voltage angles are determined in real-time. 
     
     
         28 . The method according to  claim 1 , wherein the Thévenin equivalent comprises a Thévenin voltage and a Thévenin impedance, and wherein determined Thévenin voltages are re-calculated based on the calculated voltage angles of the modified Thévenin equivalents, and modified voltage angles are calculated on basis of the updated Thévenin voltages and wherein a change in voltage angle is evaluated. 
     
     
         29 . The method according to  claim 28 , wherein evaluating the change in voltage angle is performed until a convergence criterion is satisfied. 
     
     
         30 . A computer program comprising a program code configured to perform the method according to  claim 1 , when executed on a computer. 
     
     
         31 . A computer readable medium having stored thereon a program code configured to perform the method according to  claim 1 , when executed on a computer. 
     
     
         32 . A real time static security assessment system for conducting contingency analyses in a power system, the power system having a plurality of generators injecting power into a network having a plurality of nodes and a plurality of branches, the plurality of generators being represented in the network by a plurality of nodes of power injection, the system comprises:
 a data processor configured to:
 receive information of a present state of the power system, 
 determine a Thévenin equivalent for each voltage controlled node, wherein a Thévenin equivalent is determined for each voltage controlled node on the basis of the determined present state of the power system, 
 determine a representation of the network based on the determined Thévenin equivalents, 
 apply at least one contingency to the network, 
 determine a modified representation of the network, wherein the modified network representation is a representation of the network having at least one applied contingency, wherein at least one Thévenin equivalent of at least one voltage controlled node is modified due to the at least one contingency, the modified network representation being determined on the basis of the modified Thévenin equivalents, 
 calculating voltage angles of the modified Thévenin equivalents, 
 evaluating the voltage angles to determine whether the network having at least one applied contingency admits a steady state, and 
 an interface configured to output information on the static security assessment of the modified network representation of the network, wherein the information comprises the evaluated voltage angle. 
   
     
     
         33 . A method of providing information on a real time static security assessment of a power system, the power system having a plurality of generators injecting power into a network having a plurality of nodes and a plurality of branches, the plurality of generators being represented in the network by a plurality of nodes of power injection, the method comprising:
 receiving information of a present state of the power system, determining a two source Thévenin equivalent representation, where the representation includes the power system as seen from each voltage controlled node, wherein a Thévenin equivalent is determined for each voltage controlled node on basis of the determined present state of the power system, wherein the Thévenin equivalent comprises a Thévenin voltage and a Thévenin impedance,   determining a representation of the network based on the determined Thévenin equivalents,   applying at least one contingency to the network, determining a modified representation of the network representation, wherein the modified network representation of the network having at least one applied contingency, wherein at least one Thévenin equivalent of at least one voltage controlled node is modified due to the at least one contingency, the modified network representation being determined on the basis of the modified Thévenin equivalents,   calculating voltage angles of the modified Thévenin equivalents,   evaluating the voltage angle to determine whether the network having at least one applied contingency admits a steady state, and   outputting information on static security assessment of the modified representation of the network, wherein the information comprises the evaluated voltage angles.